Regex pattern for single backslash

this will help How can I build a regex example that can escape single quote and backslash in a given string for example using java? , You must use \\\\' instead \\\'.

I wish did fix the issue. I'm trying to replace all double backslashes with just a single backslash. I want to replace 'class=\\"highlight' with 'class=\"highlight'. I thought that python treats '\\' as one backslash and r'\\+' as a string with two backslashes. But when I try , why not use string.replace()?

>>> s = 'some \\\\ doubles'
>>> print s
some \\ doubles
>>> print s.replace('\\\\', '\\')
some \ doubles

>>> s = r'some \\ doubles'
>>> print s
some \\ doubles
>>> print s.replace('\\\\', '\\')
some \ doubles

help you fix your problem A backslash character (\) is considered to be an escape character by both PHP's parser and the regular expression engine (PCRE). If you write a single backslash character, it will be considered as an escape character by PHP parser. If you write two backslashes, it will be interpreted as a literal backslash by PHP's parser. But when used in a regular expression, the regular expression engine picks it up as an escape character. To avoid this, you need to write four backslash characters, depending upon how you quote the pattern.
To understand the difference between the two types of quoting patterns, consider the following two var_dump() statements:

var_dump('~\\\~');
var_dump("~\\\\~");

string(4) "~\\~"
string(4) "~\\~"

will be helpful for those in need Finally I solved it.
What I am doing here is instead of using "Regex.IsMatch()" directly,I created a Regex object and passing the dynamic value from the Sql server database i.e. ^(+44\s?7\d{3}|(?07\d{3})?)\s?\d{3}\s?\d{3}$, then check whether the input matches.

      string sRegxE =dbContext.GetFields.Where(s => s.Name == sColumnName).Select(s => s.ExpressionValue).FirstOrDefault();
      Regex RgxM = new Regex("" + sRegxE + "");
      Match isPhoneNumber = RgxM.Match(sColumnValue);
       if (isPhoneNumber.Success)
         {
           //Do somthing...
         }

it should still fix some issue If we wish to fail the double backslash, and only pass the single one, we would be simply adding more boundaries to our expression, such as we would be using start and end anchors:

^\\\s$